Web temperature control apparatus



Dec. 29, 1964 w. R. STELLING, JR., ETAL 3,153,406

WEB TEMPERATURE CONTROL APPARATUS Filed March l5,A

2 Sheets-Sheet l BY Mm,

Dec. 29, 1964 w. R. STELLING, JR., ETAL 3,163v406 WEE TEMPERATURE CONTROL APPARATUS 2 Sheets-SheerI 2 Filed March l5. 1961 mi, M/JEW//ggw AT TOE/V55 United States Patent O 3,163,406 WEB TEMPERATURE @@Nitlh APPARATUS Waiter E. Stelling, fir., Milwaukee, Wis., and Frederick H. Wittei, Cincinnati, (Ehio, assignors to Faustel, Inc., Miiwaulree, Wis., a corporation of Wisconsin Filed Mar. 15, 1961, Ser. No. 96,026 3 Claims. till. 263-3) This invention relates generally to drying ovens for webs and relates more particularly to temperature control systems for such Webs.

In equipment of the type to which the present invention relates, it is important to be able to `accurately control the temperature of the web to prevent web damage by temperatures which are too high, and on the other hand, to insure sufficient heat to properly dry the web.

Many factors affect the drying efect of the web for any setting of the oven, for example, varying moisture content or different web speeds. It is imperative to be able to immediately change the heat input to the rapidly moving web so as to provide the proper drying effect without delay and without causing the control mechanism to hunt Shortcomings of conventional drying systems include their tendency to hunt in attempting to establish Vthe proper web temperature-a slight blast of heat causing excessive web temperature rise. Other conventional systems use web temperature sensing devices which in themselves give false or inaccurate temperature readings, due in some cases, to the heat of friction developed by the moving web in contact with the sensing device.

Accordingly, the present invention provides a web temperature sensing device which will accurately measure the temperature of the web as the latter leaves the drying oven and without contacting the web.

The present invention also provides a Web temperature control system which will quickly and accurately vary the heat input to the web Without any hunting f the system. This system instantly corrects the heat input to the web as soon as the web temperature begins to change from a predetermined setting. rIhe result is an instantaneously responsive control system which accurately maintains a predetermined and constantV web temperature, regardless of varying web conditions and speed.

These and other objects and ladvantages will appear herein as the disclosure progresses, reference being had to the accompanying drawings, in which:

FIGURE 1 is a schematic diagram of a web drying oven assembly and a circuit diagram of the web temperature control system in accordance with the present invention;

FGURE 2 is a perspective view of the thermocouple unit shown in FIGURE 1, but on an enlarged scale and with parts broken away and in section for clarity in the drawings;

FIGURES 3 Vand 4 are plan and side elevational views of the contactless sensitive instrument means for use in the circuit shown in FIGURE l;

FIGURE 5 is an enlarged detail view of the loop end of the therrnocouple made in accordance with the present invention; and

FIGURE 6 is a schematice external wiring diagram of the motor operator.

Oven

Referring in greater detail to the drawings, the drying oven O is of the enclosed tunnel type having an exhaust conduit 6 extending from adjacent the entry end of the tunnel. A'series vof blast tubes 7 extend inside the tunnel and acrossits Width and act to produce a direct land lo-v calized blast of ,air on the web W as it moves rapidly through the tunnel on the idler rolls ti and in the direction indicated by the arrow in FIGURE 1. The supply conduit 9 furnishes heated air to one end of each of the tubes from the heating chamber C in which is located the burner B, to be described. If a more complete description of the structure and function of the blast tubes or oven is deemed necessary or desirable, reference may be had to the co-pending United States patent application, Serial No. 52,117 filed August 6, 1960, and entitled, Web Dryer, which issued on January 22, 1963, as U.S. Patent No. 3,074,179.

Air Supply A fan F is provided for forcing air past the burner B, through conduit 9, out of 'the tubes 7 and over the surface of the web. In the illustration shown, the burner is located on the pressure side of the fan F but of course the burner could also be located on the suction side of the fan. The yair supplied by the fan is preferably filtered `and may consist of fresh air mixed with some of the air which has been exhausted from the oven O. In other Words, the system may be of the recirculating or non-recirculating type, with the burner located on the suction or pressure side of the circulating fan.

F nel Valve Means are provided for furnishing a properly proportioned mixture of `air and fuel to the burner. This means consists of la conventional mixing or ratiov valve mechanisrn V having an air inlet opening 10 and a fuel suppiy conduit 11 for supplying fuel such as gas to the valve mechanism. The valve mechanism is located on the inlet side of the blower 12, `and the gas and air are intimately mixed and then delivered by blower 12 through its outlet conduit 12a to the burner. These ratio valves are conventional and may be of the type shown in United States Patent No. 2,286,173 issued June 9, 1942, and further description of them is not believed `to be necessary except to say that the valve mechanism serves to vary the volume of `air as received from a supply source at lany pressure, and to vary the volume of fuel as received from a supply source at any pressure, and to modify the proportioning so obtained, and to establish such modification for different stages of the feed ow of the proportioned air and fuel; by such facility, the combustible mixture ultimately resultant from said proportioning, being of consistency which is dictated bythe conditions under which the burner is operated. In short, the valve mechanism is opened or closed to vary'the amount of fuel by a linkage L to thereby vary the heat delivered by the burner.

F nel Valve Adjusting Means Means are also provided for actuating the linkage L and this means may take the form of a motor operator MO which includes an electric shaded coil motor M having a rotatable shaft 14. A link 15 is secured to one end of the shaft 14 yand is connected With linkage L for operation thereof. An `adjustable resistor or potentiometer carried by the motor has a wiper or slider 15a secured to the other,

end of shaft 14. The motor M of the operator is driven in either direction, and is connected by Wires 16, 1'7 and 17a to a relay R of the proportional position control PPC, as will more fully appear. The direction of rotation of the motor shaft 14 is determined by theY relay R of the controlV proportional position control PPC serves to position the Vshaft 14 of the motor M in proportionV to a `tem- Fatented Dec. 29, 1964' E perature change as sensed by a thermocouple T connected -by conductors T1 and TZ to the control PPC. The proportional position control PPC may .be of the type manufactured by Wheelco Division of Barber-Colman Company and as shown in Patent 2,228,163 issued January 7, 1941, and enables a vacuum tube oscillator to control a relay without requiring the engagement of contacts for controlling the oscillator. This control may utilize a relay such as shown in Patent 2,443,784 issued June 22, 1948, and a brief description `ot the control PPC will follow which is believed sutcient for purposes of this disclosure.

The apparatus and circuit shown in FIGURE 1 comprises; an oscillator circuit OS including an electron discharge gun in the form of a vacuum or oscillator tube OT, a grid leak and condenser LC in the input or grid circuit of tube OT, tuning or pick-up coils 19 and 2), and the output circuit of tube OT may be supplied from a battery 21; contactless sensitive instrument means CS to be presently described for affecting the'oscillator circuit; and an electro-responsive 'device'such as a relay apparatus R controlled by the oscillator output change for controlling the temperature to which the contactless sensitive means CS is responsive. Coils 19, 20 and the flag 29 constitute 'means for determining a deviation of temperature from a predetermined set point and generate a ljrst control signal. In order to effect operation of the polarized relay R in response to changes in the plate current of the oscillator circuit OS, a repeater or amplifier tube AT is provided. The load impedance I is common to both the output circuit of the oscillator tube and the input circuit of the repeater tube, the latter circuit extending through the potentiometer P which is connected across a suitable bias battery BB. Also included in the circuit are a radio `frequency choke coil CC, an linductance IN, and a variable condenser VC. A by-pass condenser BPC is located in the by-pass circuit which together lwith the choke coil CC prevents the iiow of high frequency oscillatory currents through the load impedance I and the battery 21, only the non-pulsating component of the plate current nov/ing through the load impedance and the battery. i

`The output circuit of the tube AT is energized from a suitable battery 21a and extends to the winding WR of the relay R. Energization ,of the winding operates the movable contact of the relay. WR constitutes means connected to the slider a to receive the position signal and to stop-turning of the adjustable valve V.

The motor M of the motor operator MO is connected to a source of energy through conductors 23, 24. The motor is also connected to the kproportionate position control by wires 116, i7 and 17a. More specifically, wires 16 and 17 are connected to the contacts of relay R, and wire 17a.k is the ground. As shown in FIGURE 6, the ground line 17a is connected to the terminal X of the terminal block TB of the motor, and lines 16 and 17 to terminals 2 and 3 respectively. The direction of motor rotation depends, of course, on the position of the relay switch, and when a circuit isforrned betweenpoints X and 2 of the block, the motor rotates in one direction; when the circuit is through points X and 3, motor'rotation in the opposite direction occurs. Thus, operation of the relay effects corresponding operation of the motor M and the motor operator to control the fuel valve V, previously described.

The contactless sensitive means CS includes a `setting pointer 13 which is manually set along a temperature scale S at the predetermined temperature at which it is desired to-hold the web. Secured' to the setting point i8 are the pair of oscillator` pick-up coils i9 and 29 between'which ows an oscillating current. The frequency of this oscillating current is changed when a metal ag 20 mounted on a temperature indicating pointer arm 22 is moved between the coils by the-slightest-temperature change as sensed by the thermocouple T. That is to say,

the sensing thermocouple T develops a millivoltage and causes the indicator flag to swing between the prepositioned oscillator pick-up coils. More specifically, fluctuations of web temperature affect the thermocouple T so as to vary the energization of the winding 25, whereby lluctuations or deviations in temperature are converted into corresponding movements of the arm 22, pivoted at 22a and its flag 26', movement of the ag being effective through the circuits shown cause the first control signal through the relay winding to .open or close the contacts of relay R, and thus actuate the motor M to control the heat input of the burner B. The winding WR of relay` R constitutes means which are responsive to temperature deviation to initiate turning of the adjustable yfuel valve V. Stated otherwise, the output of the oscillator circuit varies depending on the position of the flag in the coils and is fed to the polarized relay R.

As previously mentioned, the relay R causes the motor M to be driven in one direction or the other. An adjustable resistor or slider 15a lixed on the end of the motor shaft 14 is thus driven to match the oscillator output to the polarized relay. Stated otherwise, the resistor 15a is rotated until it picks off the same voltage as the output of the proportionate position control PPC. The wiper constitutes a means which is responsive to movement of the adjustable valve V so that the valve feeds back a positive signal to balance the control signal generated by the deviation determining means.

Thus, as the motor shaft 14 rotates, the process input will be proportioned depending on the relative position of the setting pointer v18 and the indicator arm 22. Thereby, in this modiiied `bridge type control circuit, a change in web temperature causes an electrical unbalance of the polarized relay, and this unbalance causes the motor M of operator MO to rotate in one direction or the other and correspondingly to move the valve mechanism V in a direction to restore the web temperature toward the predetermined value and bring the electrical bridge into balance.

Tlzermocouple and Holder The novel thermocouple will now be described in detail as well as the novel means lfor mounting it and sensing the temperature of the web.

The web moves through the oven at high rates of speed, for example, speeds of 200 to 6G() feet per minute are not uncommon. An air stream or air curtain is developed along the surfaces of the web and moves along with it. This curtain is in the nature of one-eighth of an inch in thickness and clings tightlyV to the web surface. In other words, there is a stratication of air adjacent the surface of the webrwhich hangs on to the web and moves along with it. It is this curtain of air that provides a good medium for sensing the temperature of the web because lwhen he web leaves the oven after traveling a considerable distance through it, the air curtain is at the same temperature as the web itself.

The therniocouple T is positioned accurately and closely adjacent to the surface of the web within the air curtain, and adjacent the discharge end of the oven. By positioning the end of the thermocouple at a distance of approximately one-thirty second of an inch from the web surface, accurate temperature readings of the web itself can be made. Y

A holder H is provided :for precisely locating the thermocouple in adjustable relationship to the web surface to thereby pick up the web air-skin temperature. This holder consists of a ber block base member 26 having two opposite sides 27 and 2S secured thereto and which have their .free edges positioned closely adjacent the web surface.v A rear wall 29 also extends from the base, member 26 to closely adjacent the web surface. The extreme end ofthe thermocouple is formed as a loo oneV portion of the loop'being constituted of a metal such as constantan 3i) and another portion of the loop being constituted of a metal such as iron 31. Both of these metals are joined together to form a hot junctionr32 where the temperature is actually sensed. By forming these two wires to dene a loop, a much more accurate sensing of the web is obtained. In other words by forming a ilat loop and having it positioned parallel to the web, the wires cover a greater portion of the width of the web and a more accurate reading is obtained at the hot juncture 32.

The loop is also positioned so that it extends in a direction in which the web is traveling so that it will not be bent, twisted or otherwise damaged if it is accidentally touched by the rapidly moving web.

As indicated, it is also necessary to precisely locate this loop relative to and closely adjacent the web, and for this purpose a coarse adjustment and a iine adjustment are provided as follows. A threaded tting 34 is securely engaged in the base member 26 and a tube 33 extends through the fitting and contains the wires T1 and T2 of the thermoicouple. An adjustable nut 37 in threaded engagement with fitting 34 acts to compress a double beveled ferrule 35 located on the tube. Thus a pressure titting is formed for the tube and allows the tube to be adjusted relative to the fitting 34 to provide the coarse adjustment. The tine adjustment for locating the thermocouple precisely relative to the web is provided by the set screw thread connection 38 between the holderV H and the bracket 39 by means of which the holder is mounted on the oven.

It is necessary to prevent the web from fluttering and for this purpose a roller 40 is positioned under the web and immediately under the thermocouple. It will be noted the extreme end of the Vthermocouple is located within the substantially enclosed chamber 41 formed by the base member and the three sides 27, 28 and 29. The air curtain rushing along with the web enters the chamber 41 via the opening 42 in the front side of the holder H. With this particular holder and thermocouple arrangement, and the shape of and proximity of the thermocouple loop end to the web, the thermocouple is very accurate in sensing the temperature of the web. The fiber block is a poor heat conductor which minimizes heat dissipation from the holder.

Rsum

By means of the present invention the sensing device T accurately measures the temperature of the web and quickly signals the proportional position control PPC when any change in web temperature begins to occur. The control PPC then immediately causes the motor operator MO to open or close the fuel valve mechanism V and thereby immediately changes theamount of heat being delivered t0 the rapidly moving web. It is this throttling action of the fuel which provides instantaneous changes inthe heat delivered to the web and eliminates any hunting in the system in maintaining the predetermined web temperature. A true proportional relationship is established between fuel input and a continuously measured web temperature.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claimingy the subject matter which is regarded as the invention.

What is claimed `and desired to be secured byV Letters Patent is:

1. In a web dryinging oven having a burner for supplying heat to the web moving therethrough, Vand an adjustable valve for supplying variable amounts of fuel to said burner to thereby vary the heat delivered to said web, a web temperature control system comprising, sensing means for measuring the temperature of said web, adjustable means connected to said valve for adjustment thereof, rst means for determining a deviation of telnperature from a predetermined set point and generating a iirst control signal, second means responsive to such deviation to initiate turning of the adjustablel means, third means responsive to the movement of the adjustable means so that the latter feeds back a position signal to balance the said control signal generated by the deviation determining means, and fourth means operatively connected to said third means to receive the position signal and to stop turning of the adjustable means at a xed predetermined position as determined by the temperature deviation from the set point.

2. In a web drying oven having a burner for supplying heat to the web moving therethrough, and an adjustable valve for supplying variable amounts of fuel to said burner to thereby vary the heat delivered to said web, a web temperature control system comprising, sensing means for indicating the temperature of said web, adjustable means connected to said valve for adjusting the latter; and an electrical proportionate position control including a vacuum tube oscillator having input and output circuits, a load impedance eifectively included in said output circuit, a vacuum tube repeater having an input circuit coupled to said load impedance to control the output circuit of said repeater in accordance withV changes in the voltage drop across said load impedance, an electro-responsive device Vhaving an operating winding effectively included in said repeater output circuit, said sensing means affecting the tuning of said oscillator circuit to vary the voltage across said load impedance whereupon said repeater causes operation of said electro-responsive device; said electro-responsive device being connected to said adjustable means for positioning the latter and consequently said valve in proportion to a web tem-l perature change as indicated by said sensing means.

3. In a Web drying oven having a burner for supplying heat to the web moving therethrough, and an adjustable valve for supplying variable amounts of fuel to said burner to thereby vary the heat delivered to said web, a web temperature control system comprising, a. thermocouple located adjacent the web discharge end of said oven for indicating the temperature of said web,- an electrical motor operator connected to said valve for adjusting the latter; and an electrical proportionate position control including a vacuum tube oscillator having input and output circuits, a load impedance effectively included in said output circuit, a vacuum tube repeater having'an input circuit coupled to said load impedance to control the output circuit of said repeater in accordance with changes in the voltage drop across said load impedance, an electro-responsive device having an operating winding effectively included in said repeater output circuit; said thermocouple affecting the tuning of saidY oscillator circuit to vary the voltage across said load impedance whereupon said repeater causes operation of said electro-responsive device, said electro-responsive device being connected to said motor operator for positioning the latter and consequently said valve in proportion to a web'temperature change as indicated by said thermocouple.

References Cited in the file of this patent UNITED STATES PATENTS y 1,691,247 Matthews Nov. 13, 1928`y 1,730,308V Thwing Oct. V1, 1929 2,056,285 Machlet Oct. 6, 1936'v 2,438,160 Green Mar. 23, 1948` 2,611,541 Gray Sept. 23, 1952 2,618,672 Cizmadia Nov. 18, 1952 `2,627,182 Quereau Feb. 3, 1953 2,664,283 Hess Dec. 29,` 1953 2,668,701 Dietrich Feb. 9, 1954 V 2,980,410 Edvar Apr; 18, 1961 2,998,966 Knight Sept. 5, 1961 

1. IN A WEB DRYINGING OVEN HAVING A BURNER FOR SUPPLYING HEAT TO THE WEB MOVING THERETHROUGH, AND AN ADJUSTABLE VALVE FOR SUPPLYING VARIABLE AMOUNTS OF FUEL TO SAID BURNER TO THEREBY VARY THE HEAT DELIVERED TO SAID WEB, A WEB TEMPERATURE CONTROL SYSTEM COMPRISING, SENSING MEANS FOR MEASURING THE TEMPERATURE OF SAID WEB, ADJUSTABLE MEANS CONNECTED TO SAID VALVE FOR ADJUSTMENT THEREOF, FIRST MEANS FOR DETERMINING A DEVIATION OF TEMPERATURE FROM A PREDETERMINED SET POINT AND GENERATING A FIRST CONTROL SIGNAL, SECOND MEANS RESPONSIVE TO SUCH 